An image forming apparatus for printing and outputting paper is provided with a paper-feeding device for supplying the paper to the image forming apparatus main body. In some cases, a paper-feeding device of such description is an optional device detachably attached to the image forming apparatus, while in other cases it is provided as standard equipment to the image forming apparatus.
A paper-feeding device for supplying paper to an image forming apparatus main body includes, for example, a paper feed conveyance path that connects to the paper feed conveyance path of the image forming apparatus main body. Paper accommodated in a paper accommodation body of the paper-feeding device is sent out from the paper accommodation body by a paper feed roller or the like onto the paper feed conveyance path; and, while being guided along the paper feed conveyance path, is supplied to the paper feed conveyance path of the image forming apparatus main body.
The paper feed conveyance path of the paper-feeding device is typically equipped with paper sensors for detecting the state of conveyance of the paper along the paper feed conveyance path. For example, paper sensors may be disposed at locations along the paper feed conveyance path, and the motor or clutch for driving various rollers such as the paper feed roller is controlled based on output values from the paper sensors. Output values from the paper sensors can also be utilized to detect paper jams along the paper feed conveyance path, and to perform other such operations.
For example, in a conventional paper-feeding device, a signal that directly reflects fluctuation of the output value of a paper sensor is outputted to the controller of the image forming apparatus main body. The controller of the image forming apparatus main body then detects the state of conveyance of the paper or performs other such operations on the basis of the signal that directly reflects the fluctuation of the output value of the paper sensor.
In this instance, as long as the paper sensor is operating normally, once the leading edge of the paper reaches the paper sensor installation location on the paper feed conveyance path, the output value of the paper sensor changes to a value showing that paper is present, and during the interval that the paper is passing by the paper sensor installation location, the paper sensor continues to output the same value. Thereafter, once the trailing edge of the paper has passed the paper sensor installation location, the output value of the paper sensor changes to a value showing that paper is not present at the paper sensor installation location.
However, when a paper sensor temporarily experiences abnormal operation while the paper is conveyed, in some instances there may be a temporary change in values outputted by the paper sensor. For example, a value showing that paper is not present may be outputted in spite of the fact that paper is currently passing the paper sensor installation location; conversely, a value showing that paper is present may be outputted in spite of the fact that paper is not currently passing the paper sensor installation location. At such times, when a signal directly reflecting fluctuation of the output value of the paper sensor is outputted to the controller of the image forming apparatus main body, a detection error arises during detection of the state of conveyance of the paper.